I am having this issue also. The email address does not have PTR, MX record. It is a dummy domain but it is routed from an IP which has all the PTR, MX, rDNS, DKIM records.
I have created a file /opt/mailcow-dockerized/data/conf/postfix/access_sender
The content is email.address.com OK
I postmap it by
docker compose exec postfix-mailcow postmap /opt/postfix/conf/access_sender
Then restarted it
docker compose restart postfix-mailcow
Not working for me.
I did tried using another box, with postfix running without mailcow, no issue.